Searching the SETI Ellipsoid with Gaia

Brief

Using the Gaia Catalog of Nearby Stars (GCNS; 331,000 stars within 100 pc), the authors solve for which stars intersect the expanding SETI Ellipsoid defined by SN 1987A, the geometric surface from which synchronized technosignature signals would arrive at Earth simultaneously with the supernova's light-travel-time delay. Gaia EDR3 distances, more than 200× more precise than Hipparcos, reduce timing uncertainties below 1 year for the majority of the sample. At mid-2022, 134 GCNS stars lie within 0.1 light-year of the Ellipsoid surface; cross-matching all stars that crossed the Ellipsoid since Gaia's 2014 launch (5,658 sources) against the Gaia Science Alerts archive recovered no compelling variability events. An additional 278 classical novae were analyzed as alternative synchronizing events, yielding 36,135 individual stars intersecting at least one nova SETI Ellipsoid, though the authors judge this count too large for targeted follow-up.

Metadata

Category

Search

Venue

The Astronomical Journal

Type

Peer-reviewed

Year

2022

Authors

James R. A. Davenport, Barbara Cabrales, Sofia Sheikh, Steve Croft, Andrew P. V. Siemion, Daniel Giles, Ann Marie Cody

DOI

10.3847/1538-3881/ac82ea

arXiv

2206.04092

Access

Open access

Length

2.5 M

Programs

Breakthrough Listen

Instruments

Gaia EDR3, Gaia Science Alerts

Data sources

Gaia Catalog of Nearby Stars (GCNS), Gaia EDR3, Gaia Science Alerts archive, Bill Gray galactic novae catalog

Tags

SETI, technosignature, stellar astrometry, signal synchronization, target selection

Key points

• At mid-2022, 134 GCNS stars are within 0.1 light-year of the SN 1987A SETI Ellipsoid surface, the highest-priority targets for a synchronized-signal monitoring campaign.p.5
• An average of 734 stars per year within the 100 pc GCNS volume cross the SN 1987A Ellipsoid, approximately 10% of which have Gaia distance uncertainties better than 0.1 lyr.p.6
• Fewer than 8% of the 331k GCNS stars are currently inside the SN 1987A Ellipsoid, meaning over 90% remain viable future targets.p.1
• 4% of GCNS stars (13,789 sources) carry symmetrized distance uncertainties below 0.1 lyr; 54% are below 1 lyr, enabling crossing-time precision at the sub-year level.p.5
• Cross-matching 5,658 stars that crossed the SN 1987A Ellipsoid during the Gaia mission against the Gaia Science Alerts archive produced no compelling match; the closest alert was 63 arcsec away.p.6
• 278 galactic novae with Gaia EDR3 distances were analyzed; their SETI Ellipsoids intersect 36,135 individual GCNS stars, with 5,045 stars crossing two or more Ellipsoids simultaneously.p.8
• 16 of the 278 nova SETI Ellipsoids returned a Gaia Science Alert match, but all were classified as flare or cool star events; the authors conclude none represent synchronized signals.p.8
• The authors recommend the 13,789 GCNS stars with sub-0.1 lyr distance uncertainties (median G = 12.3 mag) as a priority list for technosignature monitoring campaigns.p.9

Verbatim

• “Less than 8% of stars within the 100 pc sample are inside the SN 1987A SETI Ellipsoid, meaning the vast majority of nearby stars are still viable targets for monitoring over time.”

  p.1

• “We find an average of 734 stars per year within the 100 pc volume will intersect the Ellipsoid from SN 1987A, with ∼ 10% of those having distance uncertainties from Gaia better than 0.1 lyr.”

  p.1

Most interesting

• SN 1987A exploded more than 35 years before this paper was written, yet its SETI Ellipsoid has barely begun to sweep the solar neighborhood, the supernova's signal coordination window is only just opening for nearby stars.
• The geometry of the SETI Ellipsoid is mathematically identical to the equations used to model light echoes around supernovae, a tool repurposed wholesale from classical observational astrophysics.
• The oldest nova in the 278-event catalog is Nova 1670 (CK Vul), observed over 350 years ago; its SETI Ellipsoid has been expanding for centuries and still intersects stars within the GCNS sample.
• 5,045 stars currently sit on two or more nova SETI Ellipsoids simultaneously, making them doubly prioritized targets under a multi-event synchronization strategy.
• Gaia EDR3 improved parallax precision 30% over the prior release and delivers more than 200× better astrometry than Hipparcos, directly converting into sub-year timing windows for Ellipsoid crossings.
• The authors note that galactic novae occur at roughly 50 per year, making nova-based SETI Ellipsoids a continuously refreshing target generator, but one that floods the candidate list with over 36,000 stars, limiting its practical utility for targeted campaigns.